Income Taxes - Income Tax Expense (Details) - USD ($) $ in Thousands	12 Months Ended
	Apr. 30, 2020	Apr. 30, 2019	Apr. 30, 2018
Current:
Federal	$ 295	$ 184	$ 2,298
State	370	334	743
Total current income tax expense	665	518	3,041
Deferred:
Federal	(513)	256	321
State	(96)	64	300
Total deferred income tax expense	(609)	320	621
Income tax expense	$ 56	$ 838	$ 3,662